FR2656950A1 - METHOD FOR SUPPLYING ELECTRICAL POWER WITH RESISTANCE, ELECTRICAL CIRCUIT, AND USES THEREOF - Google Patents

Abstract

The invention relates to a system for processing an electrical power supply signal for a resistive heating element. The circuit provided comprises an a.c. current source, a rectifier and a chopper for supplying the resistive element with a current having two superimposed components one being d.c. and the other being a.c., both at a variable voltage. The invention applies particularly to the supplying, with a signal thus processed, of the resistive element of a connecting piece for electro-weldable plastic tubes, of an electro-heating envelope for the connection or protection of pipes, or of a heat-shrink sheath for operation on a cable having a conductor or conductors used for the carrying of electrical energy or for telecommunications.

Description

The object of the invention is to propose a new type of feed in

  electrical energy of an electrical heating resistor with a processed signal, in particular making it possible to improve the heating conditions by Joule effect of the resistance and to greatly reduce the weight of the devices equipped with a power supply circuit

  corresponding, generator type.

  The invention finds particular application in the field of gas and the distribution of water or the flow of wastewater for the supply of electrical energy accessories generally referred to as "electrofusion", mainly intended for the construction or repair of networks of plastic pipes, such as high density polyethylene (density usually between 920 and 950 kg / m 3) or even polypropylene Still in the same field, the invention can be used for the supply of electro-heating accessories, in particular heat-shrinkable, for the repair of cast iron or steel pipes, or to ensure their heterogeneous assembly (different materials). Another preferred application of the invention relates to the field of industrial electricity, in particular for the supply of thermomouldable accessories for the protection, rehabilitation or maintenance of electrical cables or power grids.

  telecommunications, as will be seen in more detail below.

  after. Of course, there are already on the market different systems to feed a resistance of

  heating with the desired electrical energy.

  Known systems operate to supply, from a 110 or 220 volt AC source, a voltage generally lowered in a range of about 12 to 50 volts, via an induction transformer. electromagnetic

a self-transfactor.

  Since such power supply systems must be able to be used in the field, the alternating current sources usually consist of a construction generator or a "portable" generator, capable of delivering on the order of 2 to 4 kwatts with a weight generally of the order of 20 to 25 k 3,

  that is, in fact heavy and bulky.

  Another disadvantage of known systems is that they reinject current harmonics into the network used to supply the resistor. The disturbances that also appear in voltage harmonics can even lead to significant derating of the generator between the nominal power and the voltage.

power effectively usable.

  The object of the invention is to solve these problems by proposing a solution making it possible to substantially reduce the difference between the nominal power and the usable power, to reduce the reinjection of harmonics in a very large proportion, and to limit substantially the weight of the system. of power as a whole and to ensure control of the power of

  heating of the electrical resistance.

  For this purpose, the invention firstly proposes a method intended to process an electrical supply signal of a heating resistor, this process being characterized in that: from an AC source, one rectifies the current delivered by said source to obtain a unidirectional signal, and this signal is processed to deliver a processed signal comprising two superimposed components of variable voltage current, one continuous, the other alternative, and the heating resistor is supplied

with said processed signak.

  In addition to this method, the invention also relates to the supply circuit as such intended to supply electrical energy to the heating resistor considered. This circuit is characterized according to the invention in that it comprises a current source. alternatively, a current rectifier adapted to deliver a unidirectional signal, and a clean chopper to deliver at the terminals of said resistor a current with two components superimposed one continuous, the an alternative, both with variable voltage. And the invention also relates to the use of this circuit for supplying with such a processed signal the electrical resistance of a sheath or a connection or repair sleeve used on pipes where a gas fluid or gas can circulate. water (clean or used), or on electrical or telecommunications cables. Other features and benefits of

  the invention will still appear from the description that will

  follow with reference to the accompanying drawings given by way of example and in which: Figure 1 is a block diagram of a type of electrical circuit according to the invention for supplying a heating resistor with a signal cut to relatively high frequency component, Figure 2 is a diagram illustrating the application of the invention to the connection by welding thermoplastic tubes, via an electro-welded connection piece, Figure 3 schematically shows yet another application of the invention used for the insulation of metal tubes by means of an electro-shrinkable encapsulating shell with heat-shrinkable material, FIGS. 4 a and 4b still schematically illustrate yet another application of the invention. invention to the repair of two metal pipes with male-female abutment ends, via a thechase electrochauffer and furthermore, FIG. 5 schematically shows a further application of the invention in the context of an intervention on a wire rope used for the transport of electrical energy or

telecommunications.

  Referring first of all to FIG. 1, the typical circuit provided for in the invention is illustrated to provide a frequency division of a voltage from a rectified signal originating from a source of alternating current, so as to deliver to a heating electrical resistance 2 a processed signal having two superimposed current components, one continuous, the other alternative, both variable voltage. More specifically, the circuit shown firstly comprises an alternating current source 4 which can be constituted by a site generator capable of delivering a voltage of the order of, for example, 200 to 240 volts with a possible frequency of 50 to 60 hertz. . For safety, a contactor with differential protection 6 protects the circuit via two switches 8, 10 respectively provided on the ground line 12 and on the supply line 14, with interposition on this

last of a fuse 16.

  At 18, there is shown a clean current rectifier to deliver from the alternating current that it receives a unidirectional signal in the direction of a filter element such as a capacitor 20 mounted between the power supply and the output lines. mass of the rectifier 18> As a rectifying element, it is possible to

  example used a single-phase bridge.

  At the output of the filtering capacitor 20, the rectified unidirectional signal is processed by a chopper-type static converter 22 that can therefore output, at the terminals 24 and 26 of the electrical resistor 2, a two-component current associated with one continuous, the other alternative, both with variable voltage V normally less than or equal to the voltage U

  at the terminals of the source 4 of alternating current.

  As a general rule, the voltage V may vary between 10 and 110 volts, and will generally be included, especially in the context of an application to the field

  gas, between 10 and 50 volts approximately.

  As is clearly illustrated in FIG. 1, the chopper 22 firstly comprises, connected in series between the rectified power supply line and the ground line of the circuit, a shunt resistor 28 (or shunt) ) for the measurement of the current flow, one of the terminals is connected to the ground line and the other terminal is connected to a switching element 30 forming a unidirectional conduction voltage regulator, itself connected by the one of its terminals to the anode of a diode 32 "free wheel" whose cathode is connected to the rectified power supply line A

  the anode of diode 32 is still connected a self-

  induction 34 connected by its other terminal to the terminal 26 of the resistor 2, this self-induction making it possible to act on the amplitude of the regulated current as a function of the frequency

switching of the regulator 30.

  The regulator 30 which can be constituted by a transistor such as a "Darlington power" is, for its operation, placed under the control of means of

  control forming the analog control stage 36.

  These control means comprise firstly a differential amplifier 38 whose inputs 40, 42 are connected to the output of the chopper, that is to say to the

terminals 24 and 26.

  At the output of the differential amplifier 38, the corresponding signal then passes into an RMS converter 44 and then into a PID amplifier (proportional / integral / differential) 46 to be subsequently received in an analog / digital converter 48

  constituting the control circuit of transistor 30, that is

  its switching frequency, the current output, its supply voltage and its

operation on / off.

  The control block 36 thus constituted being of a conventional structure, it will not be described further. It will simply be noted again that the control unit 48 is of course connected at 50 and 52 respectively to the supply and ground lines of the circuit and that its complementary terminals 54 and 56 are respectively connected to the transistor 30 and to a point 58 of connection to the link between the resistor 28 and the

transistor 30.

  It will also be noted that, for safety reasons, a protection diode 60 connected by its anode to the ground line and by its cathode to the connection line between the self-induction 34 and the connection terminal 26 of the heating resistor is provided. 2 that the present circuit must feed.

  From the structural description that has just been

  of the circuit, it is clearly apparent that it will be possible, in accordance with the invention, to regulate the output voltage supplied across the resistor 2 with a relatively high frequency switching of the voltage (predicted a priori between 1 and About 100 K Hz) and superposition of the signal processed by the chopper 22 in two components respectively continuous and alternating, adjustable> By-possible control of the AC component of this current, and in the case where the resistor 2 will consist of a wire or in an electrically conductive cable, it will thus be possible to concentrate at the periphery of the wire the energy or the heating power delivered to the resistor, improving or at least thus favorably modifying the melting characteristics of the material in which this resistance will usually be disposed. given the privileged fields of application of

  the invention that we will now quickly present.

  Before that, we still note three advantages inherent to the invention, namely: the possible increase, compared to conventional power supply generators, the amplitude of the wave signal used as a component of the signal delivered to the resistor 2 , the reduction of the current harmonic reinjection on the power supply network of the resistor, and the possibility of proposing generators of a clearly reduced weight, of the order of 4 to 5 kilos for a power of the order from 3 to 5 k W and a voltage

  delivered at the output of the order of 50 volts.

  Let us now look at Figure 2 to see illustrated a first example of preferred application of the invention, namely the supply of an electrofusion accessory for the realization or repair of plastic pipes (and more particularly thermoplastic material) used for

the distribution of natural gas.

  In this FIG. 2, the entire electrical circuit of FIG.

  the invention illustrated in FIG.

  In this case, the two terminals 24 and 26 of the circuit 1 are connected to two connecting lugs 62 and 64 for the connection of the resistor 2, which is in the present case in the form of a wound electrical wire arranged to immediate proximity of the inner connecting surface 66 of the connecting piece of the electrofusion accessory 68, which is in the form of a sleeve whose inner orifice receives relatively closely two tubes 70 and 72 inserted end-to-end inside the sleeve so as to each have a junction surface 70a, 72a in correspondence of the

  connecting surface 66 of the orifice of the sleeve.

  Among the plastics that can be used to produce the tubes to be joined and the body of the accessory 68, there may be mentioned polyethylene, polyamide,

polybutylene and polypropylene.

  In a quite conventional manner, the welding operation for the connection of the tubes is effected by circulating the current in the coil, this current heating the resistance by joule effect and thus causing the softening until melting under pressure of the material.

surrounding plastic parts.

  For the control of this welding, it will be noted again in FIG. 1 that the accessory 68 has been equipped with two sensors 74 and 76, one end of which plunges into a cavity, respectively 78 and 80, formed in the outer surface of the sleeve until in the vicinity of the part of the

  resistance next to it.

  During heating, the surrounding plastic material brought to its molten state will be able, under the effect of pressure, to penetrate into the cavities and act on the sensors 74 and 76, which may for example consist of microswitches or optical sensors capable of detecting variations in the physical state of the material within the cavities, so as to cause the interruption of the heating by interruption of the electrical energy delivered to the resistor 2, as soon as

  the welding conditions will have been reached.

  For this purpose, it has also been provided, on the conductor 82 which powers the terminal 62 of the resistor, to interpose a control box such as 84 comprising a manually-engaged relay 86 via the push-button 88 and whose trigger is automatically controlled

by the sensors 74 or 76.

  Of course, other means of controlling the time during which the electrical resistance is powered

  in energy could have been planned.

  In FIG. 3, the case of the application of the circuit of the invention to the supply of an electro-heating accessory 90 intended for the coating of metal pipes, for example made of steel, widely used for the distribution of natural gas

(under pressure) or water.

  In this FIG. 3, the known electro-hot accessory 90 is in the form of a heat shrinkable wrapped strip which, at the point of their connection by welding, coats two pipes 97 and 99 placed end to end, and which comprises, in its thickness, an electrical heating resistor shown schematically at 92 and equipped with its two connection terminals 94 and 96 connected, of course, to the two output terminals 24 and 26 of the circuit of the invention (still identified as a whole 1), so that the current delivered by this source heats up as before by effect Joule the resistor 92 until retraction of the band 90, thus ensuring the insulation of the end part of the pipes 97 and 99 which it covers In FIG. elsewhere in FIGS. 4 a, 4 b and 5 which will follow, it will be noted that the interest relating to the control block of the heating time has not been considered.

  resistance, which is the subject of the invention.

  It should be noted that in this case the band 90 which therefore forms a kind of protective sheath for t. the thermal insulation of the pipes (with the possible addition of an insulating foam coating envelope) comprises a heat-shrinkable, meshed, plated or laminated outer coiche on a compatible inner layer 98 of compatible plastics material, such as polyethylene, which after coating of the tube, will thus connect gastight gasket the envelope of the tube, this tube and the strip

  itself to consolidate its different layers.

  The third preferred application of the invention, which has been shown diagrammatically in FIGS. 4a and 4b, relates to the repair of two pressurized gas distribution conduits 100 and 102, axially nested one inside the other by their male and female ends 102a, respectively, and whose connection must be kept gastight, via a heat-shrinkable electrocaustic envelope 104 (FIG.

4 (b), in so-called -

  As can be seen in Figure 4a, before placing the envelope, it is advisable to come to limit the gas leaks at the place of the interlocking of the tubes with a sealant seal 105 Next around this first seal there is provided another flexible gasket sealing heat-shrinkable fuse material (not shown) that will be covered by the electro-heating envelope 104 closed by its slideway 106 To ensure its function, the envelope 104 comprises an electrical heating resistor with serpentine-shaped electrical wire (s) shown at 108, and a material

  hot melt adhesion identified at 110.

  As before, to allow the shrinkage of the sheath, the connection terminals of the resistor 108 will be connected to the two outputs 24 and 26 of the circuit of the invention always schematized in 1 Before circulating the current to operate the shrinkage of the envelope, it is advisable to surround it with a removable thermal insulation cover and

  electric, provided for this purpose (not shown).

  In connection with the two preceding applications, one can also cite the quite appropriate use of the invention in connection with the joining or repair of pipes of different materials, that is to say metallic (cast, steel) and plastics material (in particular thermoplastics:

polyethylene, polypropylene).

  As in the two previous cases, use will be made of a sheath or known heat-shrinkable sleeve (not shown) correctly positioned around the joint of the pipes to be joined or repaired, the sleeve being composed of several layers of heat-shrinkable material (s). (s) reinforced with glass fibers and coated with a compatible adhesive Of course, the sleeve will be equipped with a flexible embedded heating wire, operating at the desired voltage, so as to obtain a crosslinking and irradiation bond; the adhesive providing a long-lasting seal and reinforcement by

  glass fibers providing the required mechanical strength.

  Referring now to Figure 5 to see illustrated another particular application of the invention to the power supply of a thermomouldable accessory for the protection, rehabilitation or maintenance of a cable body plastic coating wire (s) metal (s) used for the transmission of electrical energy or

telecommunications.

  In the context of this application, and as is clear from FIG. 5, the stripped end of a cable 112 with conducting wires 114 and 116 will be covered by means of an electro-heating sheath or sheath. The molded multilayer multilayered precursor comprises a heat-shrinkable portion 120 with a layer of hot-melt adhesive material and equipped with a heating resistor 122 that can be constituted by a layer of electrically conductive polymer material. Of course, to obtain the shrinkage of the sheath after having placed around the stripped end of the son with partial overlap of the insulating jacket of the cable 112, the two connection terminals 124 and 126 of the resistor 122 will be connected to the two terminal lugs 24 and 26 of the circuit supply of the invention, always shown schematically by the block 1, so as to wear, by Joule effect, the resistance to a sufficient temperature to induce radiation crosslinking with shrinkage of the sheath, thus ensuring its gastight connection with the cable 112, while allowing to reserve around the stripped son a zone forming a

  inner chamber possibly pressurizable.

  It should be noted that all types of polyethylene or lead cables, coaxial cables, with pairs or optical fibers,

  are concerned by this application.

Claims (8)

  A method for processing an electrical signal supplying a heating resistor, characterized in that: from an AC power source (4) the current delivered by said source is rectified to obtain a unidirectional signal, it is processed this signal for delivering a processed signal comprising two superimposed components of variable voltage current, one continuous, the other alternative, and the heating resistor (2,   92, 108, 122) with said processed signal.   2 circuit for supplying electrical energy to a heating resistor, characterized in that it comprises: an alternating current source (4) having at its terminals a determined voltage, a current rectifier (18) capable of delivering a signal unidirectional, and a chopper (22) capable of delivering, at the terminals of said resistor (2, 92, 108, 122), a current with two superimposed components, one continuous, the other alternative, both having a variable voltage less than or equal to said voltage across the current source alternative (4).   Circuit according to Claim 2, characterized in that the chopper comprises: a switching element (30) forming a unidirectionally conductive voltage regulator, a resistor (28), one of whose terminals is connected to a ground line (12). of the circuit and whose other terminal is connected to said switching element (30), a diode (32) whose cathode is connected to a supply line (14) of said circuit and whose anode is connected to another terminal of the switching element ( 30),   said switching element, said resistor and said diode being connected between the rectified power supply line (14) and the ground line (12), a self-induction (34) connected between the two terminals connected to each other the switching element (30) and the diode (32), and control means (36) of said element switching (30).   4 circuit according to claim 3 characterized in that the switching element (30) is a transistor. Circuit according to any one of   Claims 2 to 4 characterized in that a capacitor   (20) interposed between the rectifier (18) and the chopper (22) is connected between the supply line (14) and the line mass (12).   6 Circuit according to any one of   Claims 2 to 5, characterized in that the tension   delivered by the chopper (22) is between 10 and 110 volts, and preferably 10 and 50 volts, the frequency of the ac component of said processed signal   being between about 1 and 100 K Hz.   7 Use of the circuit according to one   any of claims 2 to 6 for feeding with   said signal processed the electrical resistance (2) of which an electroweldable connection piece (68) is provided near a joint surface (66) for its bonding by welding with cooperating surfaces (70a, 72a) of elements tubular (70, 72) of thermoplastic material   compatible with the material of the connection piece.   8 Use of the circuit according to one   any of claims 2 to 6 for feeding with   said signal treated the electrical resistance (92, 108) of which is provided in its thickness a sheath or a multilayer electro-heating protective envelope comprising a body of heat-shrinkable material (90, 104) and an inner connecting layer (98, 110) suitable for coating substantially gastight at least one pipe (97, , 102).   9 Use of the circuit according to one   any of claims 2 to 6 for feeding with   said signal processed the electrical resistance (122) which is provided in its thickness a sheath (118) with a multilayer structure comprising a heat-shrinkable portion (120) layer of hot melt material suitable for adhering on a cable (112) with plastic body d coating of wires (114, 116) for carrying energy   electric or telecommunications.